1. Field of the Invention
The present invention concerns an optical scanning apparatus for moving an optical spot to an optional position in a region observed under the visual field of a microscope.
2. Statement of the Related Art
Optical scanning apparatus, particularly, laser scanning apparatus using laser light sources have been used for laser manipulation of displacing a micro specimen captured by irradiation of a laser light to an optional position, or microscopic laser fabrication of irradiating a laser light to biological tissues under the visual field of a microscope to conduct fabrication such as heating or cutting and they have an extensive range of application use.
An existent laser scanning apparatus 21 shown in FIG. 5 has an optical system including an optical axis LX irradiated from a semiconductor laser 22 incorporating a collimator lens 24 to a condensing lens 23 for condensing the light on an observed plane OS, along which, are arranged galvano mirrors 25X and 25Y for deflecting the laser light upward or downward and leftward or rightward relative to the optical axis LX, a scanning lens 26A for refracting the laser light deflected upward and downward and leftward or rightward in parallel with the optical axis, and a second scanning lens 26B for collimating the laser beam and refracting it to the condensing lens 23.
In the constitution described above, since the first and the second scanning lenses 26A and 26B are interposed between the galvano mirrors 25X and 25Y, and the condensing lens 23, when the light displaced by inclining the galvano mirrors 25X and 25Y each at a predetermined angle is condensed by the condensing lens 23, the amount of displacement of a laser spot can be reduced and the spot can be moved by a micro distance, so that the laser spot can be scanned under the visual field of a microscope.
Generally, since the first and the second scanning lenses 26A and 26B use two convex lenses of an identical focal length f which are arranged such that respective focal positions are aligned with each other, the distance between the lenses is twice the focal lens f and the condensing lens 23 is positioned at the focal position of the second scanning lens 26B.
Usually, the distance between the first scanning lens 26A and galvano mirror 25Y is kept at or longer than the focal length f of the first scanning lens 26A or more and the distance from the galvano mirror 25X to the semiconductor laser 22 is also kept at about a focal length of the first scanning lens 26A.
Accordingly, the length of the laser scanning apparatus 21 form the semiconductor laser 22 to the condensing lens 23 requires four times the focal length to bring about a problem of increasing the size of the apparatus.
Particularly, when the laser scanning device 21 is assembled into an inverted microscope 31, it is connected with a connection port 35A (35B) formed on the side (or back) of the microscope 31 as shown in FIG. 6.
In this case, an objective 32 of the microscope 31 is used as the condensing lens 23 and a branched optical axis SX1 (SX2) branched from an optical axis MX from the objective 32 to an eyepiece 33 by a half-mirror 34A (34B) is aligned with the optical axis LX of a laser scanning apparatus 21.
Accordingly, the optical channel length from the objective 32 by way of the half-mirror 34A (34B) to the second scanning lens 26B is just equal with the focal length of the second scanning lens 26B. In this case, since it is necessary for the focal length: about f≈20 cm at the shortest, the entire length of the apparatus exceeds 1 m.
In view of the above, the present inventors et al. have experimentally manufactured a small-sized laser scanning apparatus as shown in FIG. 7. The apparatus has an optical system including an optical axis LX from a semiconductor laser 22 incorporating a collimator lens 24 for illuminating a laser light to a condensing lens 23 for condensing the irradiated light on an observed plane OS, along which are arranged a concave lens 42 for diverging the laser light, a focusing lens 43 for focusing diverged light, galvano mirrors 25X and 25Y for deflecting the focused light upward or downward and leftward or rightward relative to the optical axis LX, and a scanning lens 44 for collimating and then refracting the laser light deflected upward or downward and rightward or leftward to the condensing lens 23.
Respective optical elements are arranged so as to satisfy the relation:b=f11a/(a−f11)f13=−{f11f12/(f11−f12)−c}where f13 represents a focal length of a concave lens 42,
f12 represents a focal length of a focusing lens 43,
f11 represents a focal length of a scanning lens 44,
c represents a distance between the concave lens 42 and the focusing lens 43,
b represents a distance between the galvano mirror 25Y and the scanning lens 44, and
a represents a distance between the scanning lens 44 and the condensing lens 23.
With the constitution described above, since one scanning lens 44 may suffice, the length from the semiconductor laser 22 to the condensing lens 23 can be shortened to make the size of the entire apparatus smaller.
However, in any of the cases, since the position of the laser spot is determined by the angle of inclination of the galvano mirrors 25X and 25Y, the control is troublesome. In addition, since high accuracy is required for the alignment of optical axes upon assembling, it involves problem of making manufacture troublesome, increasing the manufacturing cost and poor yield.
Further, since existent laser scanning apparatus 21 or 41 uses large a number of lenses, the alignment for optical axes is troublesome by so much and, particularly, high accuracy is required for the alignment of optical axes with the galvano mirrors 25X and 25Y.
In view of the above, the present invention has a technical subject of providing an optical scanning apparatus which is small in the size and simple in the structure, can be controlled easily, requires no high accuracy for the alignment of the optical axes, and can reduce the manufacturing cost as well.